U.S. patent number 8,835,548 [Application Number 13/496,410] was granted by the patent office on 2014-09-16 for process for producing crosslinked, melt-shaped articles.
This patent grant is currently assigned to Union Carbide Chemicals & Plastics Technology LLC. The grantee listed for this patent is Jeffrey M. Cogen, Mohamed Esseghir, Saurav S. Sengupta. Invention is credited to Jeffrey M. Cogen, Mohamed Esseghir, Saurav S. Sengupta.
United States Patent |
8,835,548 |
Esseghir , et al. |
September 16, 2014 |
Process for producing crosslinked, melt-shaped articles
Abstract
Crosslinked, melt-shaped articles are manufactured by a process
that does not require the use of post-shaping external heat or
moisture, the process comprising the steps of: A. Forming a
crosslinkable mixture of a 1. Organopolysiloxane containing one or
more functional end groups; and 2. Silane-grafted or
silane-copolymerized polyolefin; and B. Melt-shaping and partially
crosslinking the mixture; and C. Cooling and continuing
crosslinking the melt-shaped article. Crosslinking is promoted by
the addition of a catalyst to the mixture before or during
melt-shaping or to the melt-shaped article.
Inventors: |
Esseghir; Mohamed (Monroe
Township, NJ), Cogen; Jeffrey M. (Flemington, NJ),
Sengupta; Saurav S. (Somerset, NJ) |
Applicant: |
Name |
City |
State |
Country |
Type |
Esseghir; Mohamed
Cogen; Jeffrey M.
Sengupta; Saurav S. |
Monroe Township
Flemington
Somerset |
NJ
NJ
NJ |
US
US
US |
|
|
Assignee: |
Union Carbide Chemicals &
Plastics Technology LLC (Midland, MI)
|
Family
ID: |
43066821 |
Appl.
No.: |
13/496,410 |
Filed: |
September 14, 2010 |
PCT
Filed: |
September 14, 2010 |
PCT No.: |
PCT/US2010/048720 |
371(c)(1),(2),(4) Date: |
March 15, 2012 |
PCT
Pub. No.: |
WO2011/034836 |
PCT
Pub. Date: |
March 24, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120178867 A1 |
Jul 12, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61242857 |
Sep 16, 2009 |
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Current U.S.
Class: |
524/504;
174/110SR; 524/266; 525/479; 525/69 |
Current CPC
Class: |
B29C
67/24 (20130101); C08K 5/57 (20130101); H01B
3/22 (20130101); C08L 51/06 (20130101); H01B
3/307 (20130101); C08L 23/08 (20130101); B29C
45/0001 (20130101); B29C 45/16 (20130101); C08L
43/04 (20130101); C08F 220/10 (20130101); H01B
19/00 (20130101); C08J 3/24 (20130101); C08L
83/06 (20130101); C08L 83/04 (20130101); H01B
3/46 (20130101); H01B 7/00 (20130101); C08J
3/246 (20130101); C08L 23/04 (20130101); B29C
70/88 (20130101); C08J 3/244 (20130101); C08L
83/04 (20130101); C08L 83/00 (20130101); C08L
83/06 (20130101); C08L 23/08 (20130101); C08L
23/08 (20130101); C08L 83/06 (20130101); C08L
2207/322 (20130101); C08L 83/04 (20130101); C08L
43/04 (20130101); C08K 5/57 (20130101); B29K
2023/06 (20130101); B29K 2105/0088 (20130101); B29K
2023/0625 (20130101); B29K 2995/0097 (20130101); B29K
2105/0014 (20130101); C08L 2203/202 (20130101); B29L
2009/00 (20130101); C08J 2383/04 (20130101); C08L
2207/322 (20130101); B29K 2105/0085 (20130101); C08G
77/442 (20130101); C08J 2423/04 (20130101); B29K
2023/18 (20130101); B29K 2105/0067 (20130101); C08G
77/16 (20130101); B29K 2105/24 (20130101); B29K
2995/0083 (20130101); B29L 2031/3462 (20130101) |
Current International
Class: |
C08L
83/04 (20060101); C08L 51/06 (20060101); H01B
3/30 (20060101); H01B 3/44 (20060101); H01B
3/46 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1018533 |
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Jul 2000 |
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EP |
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2640129 |
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Aug 1997 |
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JP |
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9319104 |
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Sep 1993 |
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WO |
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9500526 |
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Jan 1995 |
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WO |
|
9514024 |
|
May 1995 |
|
WO |
|
9810724 |
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Mar 1998 |
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WO |
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9849212 |
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Nov 1998 |
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WO |
|
Other References
Machine Translation of JP 2640129 B2. Aug. 13, 1997. cited by
examiner.
|
Primary Examiner: Boyle; Robert C
Assistant Examiner: Rieth; Stephen
Attorney, Agent or Firm: Whyte Hirschboeck Dudek S.C.
Parent Case Text
PRIORITY
This application claims priority to U.S. Patent Application No.
61/242,857 filed on Sep. 16, 2009, the entire content of which is
incorporated by reference herein.
Claims
What is claimed is:
1. A process for the manufacture of crosslinked, melt-shaped
articles, the process comprising the steps of: A. Forming a
crosslinkable mixture comprising: 1. at most 10 wt %, based on the
total weight of the crosslinkable mixture, of an organopolysiloxane
containing two functional end groups which are hydroxyl groups,
wherein the organopolysiloxane is a polydimethylsiloxane of the
formula ##STR00003## wherein Me is methyl and n is from 10 to 400;
and 2. Silane-grafted polyethylene; B. Melt-shaping and partially
crosslinking the mixture into an article; and C. Cooling the
melt-shaped article; and D. Storing the melt-shaped article and
continuing crosslinking without external moisture diffusion,
wherein a crosslinking catalyst is added to the mixture before or
during melt-shaping or to the melt-shaped article, wherein the
melt-shaped article has a thickness of greater than 0.2 mm, and
wherein the crosslinked, melt-shaped article passes the hot creep
test (100% elongation) measured at 200.degree. C., 0.2 MPa load
held for 15 minutes in accordance with IEC 60811-2-1.
2. The process of claim 1 in which the catalyst is a Lewis or
Bronsted acid or base.
3. The process of claim 1 in which the crosslinkable mixture
comprises, based on the weight of the mixture: i. 0.5 to 10 wt % of
the organopolysiloxane; and ii. 0.01 to 0.2 wt % of the
crosslinking catalyst.
4. The process of claim 1 in which at least one of the
crosslinkable mixture or a component of the mixture is subjected to
drying conditions prior to melt shaping the crosslinkable
mixture.
5. The process of claim 1 in which at least one of the
organopolysiloxane and crosslinking catalyst is at least partially
soaked into the silane-grafted polyethylene at a temperature below
the melting temperature of the silane-grafted polyethylene prior to
melt-shaping the mixture.
6. The process of claim 1 in which the crosslinking catalyst is a
Bronsted acid.
7. The process of claim 6 in which the crosslinking catalyst is
sulfonic acid.
8. The process of claim 1 in which the melt-shaped article is a
cable coating.
Description
FIELD OF THE INVENTION
This invention relates to crosslinked, melt-shaped articles. In one
aspect, the invention relates to a process for producing
crosslinked, melt-shaped articles while in another aspect, the
invention relates to such a process in which the articles are
crosslinked using an organopolysiloxane containing two or more
functional end groups. In yet another aspect, the invention relates
to such a process in which the crosslinking is accomplished without
requiring the use of post-shaping external heat or moisture.
BACKGROUND OF THE INVENTION
Compositions used in the manufacture of crosslinkable articles,
such as heat resistant wire & cable coatings and molded parts
and accessories, typically require cross-linking after final
shaping. Various crosslinking methods are practiced in the art, two
of which are in wide usage, i.e., peroxide crosslinking and
moisture cure (the latter of which usually employs a silane grafted
or copolymerized polyolefin).
Moisture cure systems have the advantage in that they can be
processed within a wide range of melt temperatures but are
generally limited to thin wall constructions because the
crosslinking relies on diffusion of external moisture into the
article. Peroxide cure compositions are preferred for thick wall
constructions, e.g. medium voltage (MV) cable insulation and molded
cable accessories. These curable compounds need to be processed at
temperatures which are below the peroxide decomposition temperature
in order to avoid premature crosslinking (scorch) prior to forming
the article. Once the article is formed, it needs to be heated
uniformly to the peroxide decomposition temperature, and then held
at that temperature for the time necessary to achieve the desired
level of crosslinking. This can keep the production rate for such
articles low due to poor heat transfer through the article walls.
Furthermore, once the article is cooled, peroxide decomposition
slows down to negligible levels; thus any significant crosslinking
comes to an end. The combined problems of scorch and long heating
and cure times (whether in-mold cure time or residence time in a
continuous vulcanization tube) lead to long manufacturing cycles,
and thus low productivity (units per time).
BRIEF SUMMARY OF THE INVENTION
In one embodiment the invention is a process for the manufacture of
crosslinked, melt-shaped articles, the process comprising the steps
of:
A. Forming a crosslinkable mixture comprising: 1.
Organopolysiloxane containing two or more functional end groups;
and 2. Silane-grafted or silane-copolymerized polyolefin;
B. Melt-shaping and partially crosslinking the mixture into an
article; and
C. Cooling and continuing crosslinking the melt-shaped article.
The process does not require the use of post-shaping external heat
and/or moisture although either or both can be used if desired.
Crosslinking can be promoted by the addition of a catalyst to the
mixture before or during melt-shaping, or to the melt-shaped
article (e.g., by diffusion from an adjoining layer if the article
is a layer in a multilayer construction. Surprisingly, compounding
a mixture containing these components produces a stable
thermoplastic composition which can be shaped and partially
crosslinked by melt processing into an article, but upon storage at
ambient conditions undergoes thorough crosslinking without the need
for external moisture or heat. At a microscopic scale the
morphology of such a blend shows greater compatibility between the
silicone and the polyolefin phases compared to either a physical
(unreacted) siloxane/polyolefin blend or a physical, i.e.,
unreacted, blend of a siloxane and a silane-grafted polyolefin.
The process of this invention eliminates the reliance on external
moisture diffusion that is required in conventional moisture cure.
The process of this invention is particularly useful for
manufacturing thick-wall (greater than (>) 0.2, more typically
>0.5 and even more typically >1, millimeter (mm)),
crosslinked constructions such as in high and medium voltage cable
insulation, wire and cable molded elastomeric connectors and
accessories, and molded automotive heat resistant parts. In the
case of injection molded parts, after injection in a mold and once
the article is formed, the compositions do not require additional
heating or holding times to cure. Rather, the article can be cooled
to achieve green strength to retain the desired shape as is common
in thermoplastic injection molding operations. Once removed from
the mold, the cure step continues off mold to achieve full cure.
This approach improves manufacturing cycle time and achieves higher
productivity (units per time).
In one embodiment hydroxyl-terminated silicone is reacted with an
alkoxy silane (or silanol) that is grafted to a polyolefin or other
polymer. Methods for preparation of such grafted polymers are well
known. For example, vinyltrimethoxysilane (VTMS) can be grafted to
polyethylene using peroxide. Also, various reactor copolymers are
available, such as SI-LINK.TM., which is a copolymer of VTMS and
ethylene available from The Dow Chemical Company.
Silicone polymers with hydroxyl end groups are readily available.
Reactions of these silicones directly with grafted alkoxysilanes or
silanols provide an interesting range of approaches, including:
A. Crosslinking via direct reaction (at high levels for network
formation or low level coupling for melt strength enhancement
through long chain branches);
B. Formation of silicone-functionalized polyolefins by operating
under conditions that do not result in formation of a crosslinked
network (e.g. use of monohydroxyl silicone or very low levels of
dihydroxy silicone, or low graft levels on the polymer); if a
suitable amount of SiOR remains in the system after
functionalization, subsequent moisture crosslinking is possible;
and
C. Silane-grafted polyolefins can be dynamically crosslinked in the
presence of polyolefins that do not contain grafted silane to make
thermoplastic vulcanizates (TPV) using silicone-mediated
crosslinking reactions.
In one embodiment the invention is a process for the manufacture of
crosslinked, melt-shaped articles, the process comprising the steps
of:
A. Forming a crosslinkable mixture comprising: 1.
Organopolysiloxane containing two or more functional end groups; 2.
Polyolefin; 3. Silane; and 4. Peroxide;
B. Melt-shaping the mixture into an article at conditions
sufficient to graft the silane to the polyolefin and to partially
crosslink the silane-grafted polyolefin; and
C. Cooling and continuing the crosslinking of the article.
This embodiment combines the silane grafting of the polyolefin and
the initiation of the crosslinking of the mixture into a single
step.
In one embodiment the invention is a process for the manufacture of
crosslinked, melt-shaped articles, the process comprising the steps
of: 1. Preparing a silane-grafted polyolefin; 2. Mixing the
silane-grafted polyolefin with a hydroxy-terminated
polydimethylsiloxane; 3. Melt-shaping the mixture into a storage
article; 4. Introducing the storage article to a second
melt-shaping operation in which the storage article is melt-shaped
into a finished article; 5. Introducing a crosslinking catalyst
during or after the second melt-shaping operation; and 6. Cooling
and crosslinking the finished article from the second melt-shaping
operation. This embodiment allows for the decoupling of the
mixture-forming steps from the melt-shaping and crosslinking steps
thus allowing the process to be performed over different spaces and
times. The storage article is typically pellets which are re-melted
and optionally mixed with a crosslinking catalyst to form the
finished molded or extruded article.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a graph reporting the data from a dynamic mechanical
analysis (DMA) of an ENGAGE plastomer and an ENGAGE plastomer
reactively modified with hydroxyl-terminated polydimethylsiloxane
(PDMS).
FIG. 2 is a schematic of a cross-section of a molded electrical
connector comprising a thick-wall insulation layer sandwiched
between two semiconductive layers.
FIG. 3 is a graph reporting the DMA of the insulation layer of FIG.
2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Unless stated to the contrary, implicit from the context, or
customary in the art, all parts and percents are based on weight
and all test methods are current as of the filing date of this
disclosure. For purposes of United States patent practice, the
contents of any referenced patent, patent application or
publication are incorporated by reference in their entirety (or its
equivalent US version is so incorporated by reference) especially
with respect to the disclosure of synthetic techniques, definitions
(to the extent not inconsistent with any definitions specifically
provided in this disclosure), and general knowledge in the art.
The numerical ranges in this disclosure are approximate, and thus
may include values outside of the range unless otherwise indicated.
Numerical ranges include all values from and including the lower
and the upper values, in increments of one unit, provided that
there is a separation of at least two units between any lower value
and any higher value. As an example, if a compositional, physical
or other property, such as, for example, molecular weight,
viscosity, melt index, etc., is from 100 to 1,000, it is intended
that all individual values, such as 100, 101, 102, etc., and sub
ranges, such as 100 to 144, 155 to 170, 197 to 200, etc., are
expressly enumerated. For ranges containing values which are less
than one or containing fractional numbers greater than one (e.g.,
1.1, 1.5, etc.), one unit is considered to be 0.0001, 0.001, 0.01
or 0.1, as appropriate. For ranges containing single digit numbers
less than ten (e.g., 1 to 5), one unit is typically considered to
be 0.1. These are only examples of what is specifically intended,
and all possible combinations of numerical values between the
lowest value and the highest value enumerated, are to be considered
to be expressly stated in this disclosure. Numerical ranges are
provided within this disclosure for, among other things, the
component amounts of the composition and various process
parameters.
"Cable" and like terms mean at least one wire or optical fiber
within a protective insulation, jacket or sheath. Typically, a
cable is two or more wires or optical fibers bound together,
typically in a common protective insulation, jacket or sheath. The
individual wires or fibers inside the jacket may be bare, covered
or insulated. Combination cables may contain both electrical wires
and optical fibers. The cable, etc. can be designed for low, medium
and high voltage applications. Typical cable designs are
illustrated in U.S. Pat. Nos. 5,246,783, 6,496,629 and
6,714,707.
"Polymer" means a compound prepared by reacting (i.e.,
polymerizing) monomers, whether of the same or a different type.
The generic term polymer thus embraces the term "homopolymer",
usually employed to refer to polymers prepared from only one type
of monomer, and the term "interpolymer" as defined below.
"Interpolymer" and "copolymer" mean a polymer prepared by the
polymerization of at least two different types of monomers. These
generic terms include both classical copolymers, i.e., polymers
prepared from two different types of monomers, and polymers
prepared from more than two different types of monomers, e.g.,
terpolymers, tetrapolymers, etc.
"Ethylene polymer", "polyethylene" and like terms mean a polymer
containing units derived from ethylene. Ethylene polymers typically
comprise at least 50 mole percent (mol %) units derived from
ethylene.
"Ethylene-vinylsilane polymer" and like terms mean an ethylene
polymer comprising silane functionality. The silane functionality
can be the result of either polymerizing ethylene with a vinyl
silane, e.g., a vinyl trialkoxy silane comonomer, or, grafting such
a comonomer onto an ethylene polymer backbone as described, for
example, in U.S. Pat. No. 3,646,155 or 6,048,935.
"Blend," "polymer blend" and like terms mean a blend of two or more
polymers. Such a blend may or may not be miscible. Such a blend may
or may not be phase separated. Such a blend may or may not contain
one or more domain configurations, as determined from transmission
electron spectroscopy, light scattering, x-ray scattering, and any
other method known in the art.
"Composition" and like terms mean a mixture or blend of two or more
components. For example, in the context of preparing a
silane-grafted ethylene polymer, a composition would include at
least one ethylene polymer, at least one vinyl silane, and at least
one free radical initiator. In the context of preparing a cable
sheath or other article of manufacture, a composition would include
an ethylene-vinylsilane copolymer, a catalyst cure system and any
desired additives such as lubricants, fillers, anti-oxidants and
the like.
"Ambient conditions" and like terms means temperature, pressure and
humidity of the surrounding area or environment of an article. The
ambient conditions of a typical office building or laboratory
include a temperature of 23.degree. C. and atmospheric
pressure.
"Catalytic amount" means an amount of catalyst necessary to promote
the crosslinking of an ethylene-vinylsilane polymer at a detectable
level, preferably at a commercially acceptable level.
"Crosslinked", "cured" and similar terms mean that the polymer,
before or after it is shaped into an article, was subjected or
exposed to a treatment which induced crosslinking and has xylene or
decalene extractables of less than or equal to 90 weight percent
(i.e., greater than or equal to 10 weight percent gel content).
"Crosslinkable", "curable" and like terms means that the polymer,
before or after shaped into an article, is not cured or crosslinked
and has not been subjected or exposed to treatment that has induced
substantial crosslinking although the polymer comprises additive(s)
or functionality which will cause or promote substantial
crosslinking upon subjection or exposure to such treatment (e.g.,
exposure to water).
"Melt-shaped" and like terms refer to an article made from a
thermoplastic composition that has acquired a configuration as a
result of processing in a mold or through a die while in a melted
state. The melt-shaped article may be at least partially
crosslinked to maintain the integrity of its configuration.
Melt-shaped articles include wire and cable sheaths, compression
and injection molded parts, sheets, tapes, ribbons and the
like.
Ethylene Polymers
The polyethylenes used in the practice of this invention, i.e., the
polyethylenes that contain copolymerized silane functionality or
are subsequently grafted with a silane, can be produced using
conventional polyethylene polymerization technology, e.g.,
high-pressure, Ziegler-Natta, metallocene or constrained geometry
catalysis. In one embodiment, the polyethylene is made using a high
pressure process. In another embodiment, the polyethylene is made
using a mono- or bis-cyclopentadienyl, indenyl, or fluorenyl
transition metal (preferably Group 4) catalysts or constrained
geometry catalysts (CGC) in combination with an activator, in a
solution, slurry, or gas phase polymerization process. The catalyst
is preferably mono-cyclopentadienyl, mono-indenyl or mono-fluorenyl
CGC. The solution process is preferred. U.S. Pat. No. 5,064,802,
WO93/19104 and WO95/00526 disclose constrained geometry metal
complexes and methods for their preparation. Variously substituted
indenyl containing metal complexes are taught in WO95/14024 and
WO98/49212.
In general, polymerization can be accomplished at conditions
well-known in the art for Ziegler-Natta or Kaminsky-Sinn type
polymerization reactions, that is, at temperatures from
0-250.degree. C., preferably 30-200.degree. C., and pressures from
atmospheric to 10,000 atmospheres (1013 megaPascal (MPa)).
Suspension, solution, slurry, gas phase, solid state powder
polymerization or other process conditions may be employed if
desired. The catalyst can be supported or unsupported, and the
composition of the support can vary widely. Silica, alumina or a
polymer (especially poly(tetrafluoroethylene) or a polyolefin) are
representative supports, and desirably a support is employed when
the catalyst is used in a gas phase polymerization process. The
support is preferably employed in an amount sufficient to provide a
weight ratio of catalyst (based on metal) to support within a range
of from 1:100,000 to 1:10, more preferably from 1:50,000 to 1:20,
and most preferably from 1:10,000 to 1:30. In most polymerization
reactions, the molar ratio of catalyst to polymerizable compounds
employed is from 10-12:1 to 10-1:1, more preferably from
10.sup.-9:1 to 10.sup.-5:1.
Inert liquids serve as suitable solvents for polymerization.
Examples include straight and branched-chain hydrocarbons such as
isobutane, butane, pentane, hexane, heptane, octane, and mixtures
thereof; cyclic and alicyclic hydrocarbons such as cyclohexane,
cycloheptane, methylcyclohexane, methylcycloheptane, and mixtures
thereof; perfluorinated hydrocarbons such as perfluorinated
C.sub.4-10 alkanes; and aromatic and alkyl-substituted aromatic
compounds such as benzene, toluene, xylene, and ethylbenzene.
The ethylene polymers useful in the practice of this invention
include ethylene/.alpha.-olefin interpolymers having a
.alpha.-olefin content of between about 15, preferably at least
about 20 and even more preferably at least about 25, wt % based on
the weight of the interpolymer. These interpolymers typically have
an .alpha.-olefin content of less than about 50, preferably less
than about 45, more preferably less than about 40 and even more
preferably less than about 35, wt % based on the weight of the
interpolymer. The .alpha.-olefin content is measured by .sup.13C
nuclear magnetic resonance (NMR) spectroscopy using the procedure
described in Randall (Rev. Macromol. Chem. Phys., C29 (2&3)).
Generally, the greater the .alpha.-olefin content of the
interpolymer, the lower the density and the more amorphous the
interpolymer, and this translates into desirable physical and
chemical properties for the protective insulation layer.
The .alpha.-olefin is preferably a C.sub.3-20 linear, branched or
cyclic .alpha.-olefin. Examples of C.sub.3-20 .alpha.-olefins
include propene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene,
1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and
1-octadecene. The .alpha.-olefins also can contain a cyclic
structure such as cyclohexane or cyclopentane, resulting in an
.alpha.-olefin such as 3-cyclohexyl-1-propene (allyl cyclohexane)
and vinyl cyclohexane. Although not .alpha.-olefins in the
classical sense of the term, for purposes of this invention certain
cyclic olefins, such as norbornene and related olefins,
particularly 5-ethylidene-2-norbornene, are .alpha.-olefins and can
be used in place of some or all of the .alpha.-olefins described
above. Similarly, styrene and its related olefins (for example,
.alpha.-methylstyrene, etc.) are .alpha.-olefins for purposes of
this invention. Illustrative ethylene polymers include
ethylene/propylene, ethylene/butene, ethylene/1-hexene,
ethylene/1-octene, ethylene/styrene, and the like. Illustrative
terpolymers include ethylene/propylene/1-octene,
ethylene/propylene/butene, ethylene/butene/1-octene,
ethylene/propylene/diene monomer (EPDM) and
ethylene/butene/styrene. The copolymers can be random or
blocky.
The ethylene polymers used in the practice of this invention can be
used alone or in combination with one or more other ethylene
polymers, e.g., a blend of two or more ethylene polymers that
differ from one another by monomer composition and content,
catalytic method of preparation, etc. If the ethylene polymer is a
blend of two or more ethylene polymers, then the ethylene polymer
can be blended by any in-reactor or post-reactor process. The
in-reactor blending processes are preferred to the post-reactor
blending processes, and the processes using multiple reactors
connected in series are the preferred in-reactor blending
processes. These reactors can be charged with the same catalyst but
operated at different conditions, e.g., different reactant
concentrations, temperatures, pressures, etc, or operated at the
same conditions but charged with different catalysts.
Examples of ethylene polymers made with high pressure processes
include (but are not limited to) low density polyethylene (LDPE),
ethylene silane reactor copolymer (such as SiLINK.RTM. made by The
Dow Chemical Company), ethylene vinyl acetate copolymer (EVA),
ethylene ethyl acrylate copolymer (EEA), and ethylene silane
acrylate terpolymers.
Examples of ethylene polymers that can be grafted with silane
functionality include very low density polyethylene (VLDPE) (e.g.,
FLEXOMER.RTM. ethylene/1-hexene polyethylene made by The Dow
Chemical Company), homogeneously branched, linear
ethylene/.alpha.-olefin copolymers (e.g., TAFMER.RTM. by Mitsui
Petrochemicals Company Limited and EXACT.RTM. by Exxon Chemical
Company), homogeneously branched, substantially linear
ethylene/.alpha.-olefin polymers (e.g., AFFINITY.RTM. and
ENGAGE.RTM. polyethylene available from The Dow Chemical Company),
and ethylene block copolymers (e.g., INFUSE.RTM. polyethylene
available from The Dow Chemical Company). The more preferred
ethylene polymers are the homogeneously branched linear and
substantially linear ethylene copolymers. The substantially linear
ethylene copolymers are especially preferred, and are more fully
described in U.S. Pat. Nos. 5,272,236, 5,278,272 and 5,986,028.
Silane Functionality
Any silane that will effectively copolymerize with ethylene, or
graft to and crosslink an ethylene polymer, can be used in the
practice of this invention, and those described by the following
formula are exemplary:
##STR00001## in which R.sup.1 is a hydrogen atom or methyl group; x
and y are 0 or 1 with the proviso that when x is 1, y is 1; m and n
are independently an integer from 1 to 12 inclusive, preferably 1
to 4, and each R'' independently is a hydrolyzable organic group
such as an alkoxy group having from 1 to 12 carbon atoms (e.g.
methoxy, ethoxy, butoxy), aryloxy group (e.g. phenoxy), araloxy
group (e.g. benzyloxy), aliphatic acyloxy group having from 1 to 12
carbon atoms (e.g. formyloxy, acetyloxy, propanoyloxy), amino or
substituted amino groups (alkylamino, arylamino), or a lower alkyl
group having 1 to 6 carbon atoms inclusive, with the proviso that
not more than one of the three R groups is an alkyl. Such silanes
may be copolymerized with ethylene in a reactor, such as a high
pressure process. Such silanes may also be grafted to a suitable
ethylene polymer by the use of a suitable quantity of organic
peroxide, either before or during a shaping or molding operation.
Additional ingredients such as heat and light stabilizers,
pigments, etc., also may be included in the formulation. The phase
of the process during which the crosslinks are created is commonly
referred to as the "cure phase" and the process itself is commonly
referred to as "curing". Also included are silanes that add to
unsaturation in the polymer via free radical processes such as
mercaptopropyl trialkoxysilane.
Suitable silanes include unsaturated silanes that comprise an
ethylenically unsaturated hydrocarbyl group, such as a vinyl,
allyl, isopropenyl, butenyl, cyclohexenyl or gamma-(meth)acryloxy
allyl group, and a hydrolyzable group, such as, for example, a
hydrocarbyloxy, hydrocarbonyloxy, or hydrocarbylamino group.
Examples of hydrolyzable groups include methoxy, ethoxy, formyloxy,
acetoxy, proprionyloxy, and alkyl or arylamino groups. Preferred
silanes are the unsaturated alkoxy silanes which can be grafted
onto the polymer or copolymerized in-reactor with other monomers
(such as ethylene and acrylates). These silanes and their method of
preparation are more fully described in U.S. Pat. No. 5,266,627 to
Meverden, et al. Vinyl trimethoxy silane (VTMS), vinyl triethoxy
silane, vinyl triacetoxy silane, gamma-(meth)acryloxy propyl
trimethoxy silane and mixtures of these silanes are the preferred
silane crosslinkers for use in this invention. If filler is
present, then preferably the crosslinker includes vinyl trialkoxy
silane.
The amount of silane crosslinker used in the practice of this
invention can vary widely depending upon the nature of the polymer,
the silane, the processing or reactor conditions, the grafting or
copolymerization efficiency, the ultimate application, and similar
factors, but typically at least 0.5, preferably at least 0.7,
weight percent is used. Considerations of convenience and economy
are two of the principal limitations on the maximum amount of
silane crosslinker used in the practice of this invention, and
typically the maximum amount of silane crosslinker does not exceed
5, preferably it does not exceed 3, weight percent.
The silane crosslinker is grafted to the polymer by any
conventional method, typically in the presence of a free radical
initiator, e.g. peroxides and azo compounds, or by ionizing
radiation, etc. Organic initiators are preferred, such as any one
of the peroxide initiators, for example, dicumyl peroxide,
di-tert-butyl peroxide, t-butyl perbenzoate, benzoyl peroxide,
cumene hydroperoxide, t-butyl peroctoate, methyl ethyl ketone
peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane, lauryl
peroxide, and tert-butyl peracetate. A suitable azo compound is
2,2-azobisisobutyronitrile. The amount of initiator can vary, but
it is typically present in an amount of at least 0.04, preferably
at least 0.06, parts per hundred resin (phr). Typically, the
initiator does not exceed 0.15, preferably it does not exceed about
0.10, phr. The weight ratio of silane crosslinker to initiator also
can vary widely, but the typical crosslinker:initiator weight ratio
is between 10:1 to 500:1, preferably between 18:1 and 250:1. As
used in parts per hundred resin or phr, "resin" means the olefinic
polymer.
While any conventional method can be used to graft the silane
crosslinker to the polyolefin polymer, one preferred method is
blending the two with the initiator in the first stage of a reactor
extruder, such as a Buss kneader. The grafting conditions can vary,
but the melt temperatures are typically between 160 and 260.degree.
C., preferably between 190 and 230.degree. C., depending upon the
residence time and the half life of the initiator.
Copolymerization of vinyl trialkoxysilane crosslinkers with
ethylene and other monomers may be done in a high-pressure reactor
that is used in the manufacture of ethylene homopolymers and
copolymers with vinyl acetate and acrylates.
Polyfunctional Organopolysiloxane with Functional End Groups
The oligomers containing functional end groups useful in the
present process comprise from 2 to 100,000 or more units of the
formula R.sub.2SiO in which each R is independently selected from a
group consisting of alkyl radicals comprising one to 12 carbon
atoms, alkenyl radicals comprising two to about 12 carbon atoms,
aryls, and fluorine substituted alkyl radicals comprising one to
about 12 carbon atoms. The radical R can be, for example, methyl,
ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, dodecyl, vinyl,
allyl, phenyl, naphthyl, tolyl, and 3,3,3-trifluoropropyl.
Preferred is when each radical R is methyl.
In one embodiment, the organopolysiloxane containing one or more
functional end groups is a hydroxyl-terminated polydimethylsiloxane
containing at least two hydroxyl end groups. Such
polydimethylsiloxanes are commercially available, for example as
silanol-terminated polydimethylsiloxane from Gelest, Inc. However,
polydimethylsiloxanes having other terminal groups that can react
with grafted silanes may be used e.g. polydimethylsiloxanes with
amine end groups and the like. In addition, the polysiloxane may be
a moisture-crosslinkable polysiloxane. In preferred embodiments,
the polydimethylsiloxane is of the formula
##STR00002## in which Me is methyl and n is in the range of 2 to
100,000 or more, preferably in the range of 10 to 400 and more
preferably in the range of 20 to 120. Examples of suitable
polyfunctional organopolysiloxanes are the silanol-terminated
polydimethylsiloxane DMS-15 (Mn of 2,000-3,500, viscosity of 45-85
centistokes, --OH level of 0.9-1.2%) from Gelest Corp., and Silanol
Fluid 1-3563 (viscosity 55-90 centistokes, --OH level of 1-1.7%)
from Dow Corning Corp. In some embodiments the polyfunctional
organopolysiloxane comprises branches such as those imparted by
Me-SiO.sub.3/2 or SiO.sub.4/2 groups (known as Tor Q groups to
those skilled in silicone chemistry).
The amount of polyfunctional organopolysiloxane used in the
practice of this invention can vary widely depending upon the
nature of the polymer, the silane, the polyfunctional
organopolysiloxane, the processing or reactor conditions, the
ultimate application, and similar factors, but typically at least
0.5, preferably at least 2, weight percent is used. Considerations
of convenience and economy are two of the principal limitations on
the maximum amount of polyfunctional organopolysiloxane used in the
practice of this invention, and typically the maximum amount of
polyfunctional organopolysiloxane does not exceed 20, preferably it
does not exceed 10, weight percent.
Crosslinking Catalyst
Crosslinking catalysts include the Lewis and Bronsted acids and
bases. Lewis acids are chemical species that can accept an electron
pair from a Lewis base. Lewis bases are chemical species that can
donate an electron pair to a Lewis acid. Lewis acids that can be
used in the practice of this invention include the tin carboxylates
such as dibutyl tin dilaurate (DBTDL), dimethyl hydroxy tin oleate,
dioctyl tin maleate, di-n-butyl tin maleate, dibutyl tin diacetate,
dibutyl tin dioctoate, stannous acetate, stannous octoate, and
various other organo-metal compounds such as lead naphthenate, zinc
caprylate and cobalt naphthenate. DBTDL is a preferred Lewis acid.
Lewis bases that can be used in the practice of this invention
include, but are not limited to, the primary, secondary and
tertiary amines. These catalysts are typically used in moisture
cure applications.
Bronsted acids are chemical species that can lose or donate a
hydrogen ion (proton) to a Bronsted base. Bronsted bases are
chemical species that can gain or accept a hydrogen ion from a
Bronsted acid. Bronsted acids that can be used in the practice of
this invention include sulfonic acid.
The minimum amount of crosslinking catalyst used in the practice of
this invention is a catalytic amount. Typically this amount is at
least 0.01, preferably at least 0.02 and more preferably at least
0.03, weight percent (wt %) of the combined weight of
ethylene-vinylsilane polymer and catalyst. The only limit on the
maximum amount of crosslinking catalyst in the ethylene polymer is
that imposed by economics and practicality (e.g., diminishing
returns), but typically a general maximum comprises less than 5,
preferably less than 3 and more preferably less than 2, wt % of the
combined weight of ethylene polymer and condensation catalyst.
Fillers and Additives
The composition from which the crosslinked article, e.g., cable
insulation layer or protective jacket, injection molded elastomeric
connector, etc., or other article of manufacture, e.g., seal,
gasket, shoe sole, etc., is made can be filled or unfilled. If
filled, then the amount of filler present should preferably not
exceed an amount that would cause unacceptably large degradation of
the electrical and/or mechanical properties of the
silane-crosslinked, ethylene polymer. Typically, the amount of
filler present is between 2 and 80, preferably between 5 and 70,
weight percent (wt %) based on the weight of the polymer.
Representative fillers include kaolin clay, magnesium hydroxide,
silica, calcium carbonate and carbon blacks. The filler may or may
not have flame retardant properties. In a preferred embodiment of
this invention in which filler is present, the filler is coated
with a material that will prevent or retard any tendency that the
filler might otherwise have to interfere with the silane cure
reaction. Stearic acid is illustrative of such a filler coating.
Filler and catalyst are selected to avoid any undesired
interactions and reactions, and this selection is well within the
skill of the ordinary artisan.
The compositions of this invention can also contain additives such
as, for example, antioxidants (e.g., hindered phenols such as, for
example, IRGANOX.TM. 1010 a registered trademark of Ciba Specialty
Chemicals), phosphites (e.g., IRGAFOS.TM. 168 a registered
trademark of Ciba Specialty Chemicals), UV stabilizers, cling
additives, light stabilizers (such as hindered amines),
plasticizers (such as dioctylphthalate or epoxidized soy bean oil),
scorch inhibitors, mold release agents, tackifiers (such as
hydrocarbon tackifiers), waxes (such as polyethylene waxes),
processing aids (such as oils, organic acids such as stearic acid,
metal salts of organic acids), oil extenders (such as paraffin oil
and mineral oil), colorants or pigments to the extent that they do
not interfere with desired physical or mechanical properties of the
compositions of the present invention. These additives are used in
amounts known to those versed in the art.
Liquid Polymer Modifier
In an embodiment, the process includes adding a liquid polymer
modifier during the manufacture process of the crosslinked,
melt-shaped article. A "liquid polymer modifier," as used herein,
is a non-functionalized plasticizer (NFP). As used herein, an "NFP"
is a hydrocarbon liquid, which does not include to an appreciable
extent functional groups selected from hydroxide, aryls and
substituted aryls, halogens, alkoxys, carboxylates, esters, carbon
unsaturation, acrylates, oxygen, nitrogen, and carboxyl. By
"appreciable extent," it is meant that these groups and compounds
comprising these groups are not deliberately added to the NFP, and
if present at all, are present in embodiments at less than 5
percent by weight of the NFP, or less than 4, 3, 2, 1, 0.7, 0.5,
0.3, 0.1, 0.05, 0.01, or 0.001 wt %, based upon the weight of the
NFP.
In an embodiment, aromatic moieties (including any compound whose
molecules have the ring structure characteristic of benzene,
naphthalene, phenanthrene, anthracene, etc.) are substantially
absent from the NFP. In another embodiment, naphthenic moieties
(including any compound whose molecules have a saturated ring
structure such as would be produced by hydrogenating benzene,
naphthalene, phenanthrene, anthracene, etc.) are substantially
absent from the NFP. By "substantially absent," it is meant that
these compounds are not added deliberately to the compositions and
if present at all, are present at less than 0.5 wt %, preferably
less than 0.1 wt % by weight of the NFP.
In another embodiment, the NFP does not contain olefinic
unsaturation to an appreciable extent. By "appreciable extent of
olefinic unsaturation" it is meant that the carbons involved in
olefinic bonds account for less than 10% of the total number of
carbons in the NFP, preferably less than 8%, 6%, 4%, 2%, 1%, 0.7%,
0.5%, 0.3%, 0.1%, 0.05%, 0.01%, or 0.001%. In some embodiments, the
percent of carbons of the NFP involved in olefinic bonds is between
0.001 and 10% of the total number of carbon atoms in the NFP,
preferably between 0.01 and 5%, preferably between 0.1 and 2%, more
preferably between 0.1 and 1%.
In an embodiment, the liquid polymer modifier is an NFP that is a
phthalate-free hydrogenated C.sub.8 to C.sub.12 poly-alpha-olefin.
The phthalate-free hydrogenated C.sub.8 to C.sub.12
poly-alpha-olefin is naturally inert and does not affect the cure
chemistry of the crosslinkable mixture as do conventional modifiers
like mineral oil, white oil and paraffinic oils. Similarly, the
present liquid polymer modifier does not affect other chemistries,
such as, for example, antioxidant chemistry, filler chemistry,
adhesion chemistry or the like.
In addition, the present liquid polymer modifier has high
permanence, good compatibility with polyethylenes and ethylene
copolymers, and narrow molecular weight distribution (Mw/Mn or
MWD). As a result, applications using the present liquid polymer
modifier have a surprising combination of desired properties
including high cure efficiency, improved flexibility and toughness
and easy processing. Such applications display excellent surface
properties and exceptional retention of properties over time.
A nonlimiting example of a suitable liquid polymer modifier is
polymer modifier sold under the tradename Elevast, such as Elevast
R-150. Elevast polymer modifier is available from the ExxonMobil
Chemical Company, Houston, Tex.
The liquid polymer modifier advantageously replaces oil extenders
(paraffin oil and/or mineral oil) in the crosslinked, melt-shaped
article. When compared to the same crosslinked, melt-shaped article
with oil extender; a crosslinked, melt-shaped article containing
the present liquid polymer modifier unexpectedly exhibits improved
softness (i.e., lower Shore A Hardness value), increased
flexibility, (i.e., increase in M100), greater elongation, enhanced
elasticity, and improved processability (lower viscosity)--all with
no decrease in dielectric strength of the crosslinked, melt-shaped
article. The foregoing physical improvements from the liquid
polymer modifier are surprising and unexpected in view of
conventional oil extenders because oil extenders decrease
dielectric strength in the resultant crosslinked product.
Nonlimiting applications of crosslinked, melt-shaped article
containing the present liquid polymer modifier and exhibiting the
foregoing physical improvements (without loss of dielectric
strength) include wire and cable, and other applications where good
dielectric properties are required.
The liquid polymer modifier may be added during different steps of
the production process. In an embodiment, the liquid polymer
modifier is added to a crosslinkable mixture composed of (1)
organopolysiloxane (with two or more hydroxyl end groups) and (2) a
silane-grafted or silane-copolymerized polyolefin. This
crosslinkable mixture is subsequently melt-shaped, partially
crosslinked, cooled, and further cross-linked upon exposure to
ambient conditions.
In an embodiment, the liquid polymer modifier is added to a
crosslinkable mixture composed of (1) organopolysiloxane containing
two or more hydroxyl end groups, (2) polyolefin, (3) silane, and
(4) peroxide. The crosslinkable mixture is subsequently
melt-shaped, partially crosslinked, cooled and further crosslinked
when exposed to ambient conditions.
In an embodiment, the liquid polymer modifier is added with the
crosslinking catalyst. A silane-grafted polyolefin is prepared to
which a hydroxyl-terminated polydimethylsiloxane is added. The
mixture is melt-shaped into a storage article. The storage article
is introduced into a second melt-shaping operation wherein the
storage article is melt-shaped into a finished article. The process
includes introducing the crosslinking catalyst and the liquid
polymer modifier during or after the second melt-shaping operation.
The process further includes cooling and crosslinking the finished
article from the second melt-shaping operation.
Compounding/Fabrication
Compounding of the silane-functionalized ethylene polymer,
polyfunctional organopolysiloxane, catalyst, and filler and
additives, if any, can be performed by standard means known to
those skilled in the art. Examples of compounding equipment are
internal batch mixers, such as a Banbury or Bolling internal mixer.
Alternatively, continuous single or twin screw mixers can be used,
such as a Farrel continuous mixer, a Werner and Pfleiderer twin
screw mixer, or a Buss kneading continuous extruder. The type of
mixer utilized, and the operating conditions of the mixer, will
affect properties of the composition such as viscosity, volume
resistivity, and extruded surface smoothness.
The components of the composition are typically mixed at a
temperature and for a length of time sufficient to fully homogenize
the mixture but insufficient to cause the material to gel. The
catalyst is typically added to ethylene-vinylsilane polymer but it
can be added before, with or after the additives, if any.
Typically, the components are mixed together in a melt-mixing
device. The mixture is then shaped into the final article. The
temperature of compounding and article fabrication should be above
the melting point of the ethylene-vinylsilane polymer but below
about 250.degree. C.
In some embodiments, either or both of the catalyst and the
additives are added as a pre-mixed masterbatch. Such masterbatches
are commonly formed by dispersing the catalyst and/or additives
into an inert plastic resin, e.g., a low density polyethylene.
Masterbatches are conveniently formed by melt compounding
methods.
In one embodiment, one or more of the components are dried before
compounding, or a mixture of components is dried after compounding,
to reduce or eliminate potential scorch that may be caused from
moisture present in or associated with the component, e.g., filler.
In one embodiment, crosslinkable silicone-modified polyolefin
mixtures are prepared in the absence of a crosslinking catalyst for
extended shelf life, and the crosslinking catalyst is added as a
final step in the preparation of a melt-shaped article.
Articles of Manufacture
In one embodiment, the composition of this invention can be applied
to a cable as a sheath or insulation layer in known amounts and by
known methods (for example, with the equipment and methods
described in U.S. Pat. Nos. 5,246,783 and 4,144,202). Typically,
the composition is prepared in a reactor-extruder equipped with a
cable-coating die and after the components of the composition are
formulated, the composition is extruded over the cable as the cable
is drawn through the die. Cure may begin in the
reactor-extruder.
One of the benefits of this invention is that the shaped article
does not require post-shaping, e.g., after de-molding or passing
through a shaping die, cure conditions, e.g., temperature above
ambient and/or moisture from an external source such as a water
bath or "sauna". While not necessary or preferred, the shaped
article can be exposed to either or both elevated temperature and
external moisture and if an elevated temperature, it is typically
between ambient and up to but below the melting point of the
polymer for a period of time such that the article reaches a
desired degree of crosslinking. The temperature of any post-shaping
cure should be above 0.degree. C.
Other articles of manufacture that can be prepared from the polymer
compositions of this invention include fibers, ribbons, sheets,
tapes, tubes, pipes, weather-stripping, seals, gaskets, hoses,
foams, footwear and bellows. These articles can be manufactured
using known equipment and techniques.
Nonlimiting embodiments of the present disclosure are provided
below.
E1. A process for the manufacture of crosslinked, melt-shaped
articles is provided. The process comprises the steps of:
A. Forming a crosslinkable mixture comprising: 1.
Organopolysiloxane containing two or more functional end groups;
and 2. Silane-grafted or silane-copolymerized polyolefin;
B. Melt-shaping and partially crosslinking the mixture into an
article; and
C. Cooling and continuing crosslinking the melt-shaped article.
E2. The process of E1 in which a crosslinking catalyst is added to
the mixture before or during melt-shaping or to the melt-shaped
article. E3. The process of any of E1-E2 in which at least one of
the functional end groups of the organopolysiloxane is a hydroxyl
group. E4. The process of any of E1-E3 in which the crosslinkable
mixture comprises a liquid polymer modifier. E5. The process of any
of E1-E4 in which the polyolefin is a polyethylene. E6. The process
of any of E1-E5 in which the catalyst is a Lewis or Bronsted acid
or base. E7. The process of any of E1-E6 in which the crosslinkable
mixture comprises, based on the weight of the mixture:
A. 0.5 to 20 wt % of the organopolysiloxane; and
B. 0.01 to 0.2 wt % of the catalyst.
E8. The process of any of E1-E7 in which the crosslinkable mixture
further comprises at least one of a filler, plasticizing agent,
scorch retardant and moisture source. E9. The process of any of
E1-E8 in which at least one of the crosslinkable mixture or a
component of the mixture is subjected to drying conditions prior to
melt shaping the crosslinkable mixture. E10. The process of any of
E1-E9 in which at least one of the organopolysiloxane and catalyst
is at least partially soaked into the silane-grafted or
silane-copolymerized polyolefin at a temperature below the melting
temperature of the polyolefin prior to melt-shaping the
mixture.
Another process for the manufacture of crosslinked, melt-shaped
articles is provided (E11) and the process comprises the steps
of:
A. Forming a crosslinkable mixture comprising: 1.
Organopolysiloxane containing one or more functional end groups; 2.
Polyolefin; 3. Silane; and 4. Peroxide;
B. Melt-shaping the mixture into an article at conditions
sufficient to graft the silane to the polyolefin and to partially
crosslink the silane-grafted polyolefin; and
C. Cooling and continuing the crosslinking of the article.
E12. The process of E11 wherein the crosslinkable mixture comprises
a liquid polymer modifier.
Another process for the manufacture of crosslinked, melt-shaped
articles is provided (E13), the process comprising the steps of: 1.
Preparing a silane-grafted polyolefin; 2. Mixing the silane-grafted
polyolefin with a hydroxy-terminated polydimethylsiloxane; 3.
Melt-shaping the mixture into a storage article; 4. Introducing the
storage article to a second melt-shaping operation in which the
storage article is melt-shaped into a finished article; 5.
Introducing a crosslinking catalyst during or after the second
melt-shaping operation; and 6. Cooling and crosslinking the
finished article from the second melt-shaping operation.
E14. The process of E13 comprising introducing, with the
crosslinking catalyst, a liquid polymer modifier.
E15. The process of any of E1-14 in which the mixture is
melt-shaped by molding.
E16. The process of any of E1-14 in which the mixture is
melt-shaped by extrusion.
E17. A thick-walled article made by the process of any of
E1-14.
E18. An electric power cable comprising an insulation layer made by
the process of any of E1-14.
E19. An electric power cable accessory or molded connector
comprising an insulation layer made by the process of any of
E1-14.
The invention is described more fully through the following
examples. Unless otherwise noted, all parts and percentages are by
weight.
SPECIFIC EMBODIMENTS
Example 1
Table 1 reports the evaluation of several compositions. ENGAGE.TM.
8200 plastomer (an ethylene-octene copolymer of 5 MI, 0.870
density, solid pellets) is used in the experiments. The polymer
pellets are heated at 40.degree. C. for two hours then tumble
blended with a mixture of VTMS and LUPEROX 101 peroxide
(2,5-dimethyl-2,5-di(t-butylperoxy)hexane available from Arkema)
and left to soak in a glass jar using a jar roller until the
pellets are visibly dry.
A Brabender batch mixer (250 gram) is used for grafting VTMS to the
polymer. Compounding is conducted at 190.degree. C. for 15 minutes.
The grafted polymer is pressed into a plaque at room temperature
and sealed in a foil bag for subsequent experiments with
polydimethylsiloxane (PDMS).
A Brabender mixer (45 cc) is used to compound the grafted resin,
silanol-terminated PDMS and catalyst. Compounding was performed at
a set temperature of 150.degree. C. as follows: First, the mixer
was loaded with VTMS-grafted ENGAGE 8200, is fluxed and mixed for 2
minutes at 45 revolutions per minute (rpm). Silanol-terminated PDMS
(Gelest DMS-S15) is added gradually over a period of approximately
3 minutes and after addition is completed, the blend is further
mixed for 2 minutes at 45 rpm. Catalysts (DBTDL, sulfonic acid or
mixture) are then added and mixed for 15 minutes at 45 rpm. If the
resulting compound is thermoplastic, i.e. no significant
crosslinking is visible, it is pressed into a 50 mil (.about.1.3
mm) plaque immediately after removal from the mixer and stored
overnight in a sealed aluminum foil bag at 25.degree. C.
Samples are then cut to analyze for cure via hot creep analysis
(200.degree. C. oven, 15 min). Percent elongation under
20N/mm.sup.2 load is then measured. A common standard for adequate
crosslinking is elongation of less than or equal to (.ltoreq.)
100%. Measurements are obtained on triplicate samples.
TABLE-US-00001 TABLE 1 Hot Creep Test Results of Test Compositions
Component A B C D E F Si-g-PE 0 99.85 95 94.85 94.85 99.85 Sil-PDMS
5 0 5 5 5 0 Sulfonic 0 0 0 0 0.15 0.15 Acid. DBTDL 0 0.15 0 0.15 0
0 ENGAGE 95 0 0 0 0 0 8200 Total 100 100 100 100 100 100 Total
Mixing 22 15 15 21 21 15 Time (min) Hot Creep Melted Fail Fail
*Cross- Pass Fail (100% linked Elongation) prematurely *Since the
sample crosslinked prematurely, the catalyst level was subsequently
reduced as described in later examples. Si-g-PE is silane grafted
ENGAGE 8200 plastomer. Sil-PDMS is Gelest DMS-S15
silanol-terminated PDMS. Sulfonic acid is B-201 available from King
Industries. DBTDL is FASTCAT 4202 dibutyl tin dilaurate. Hot Creep
Test Percent Elongation measured at 200.degree. C., 0.2 MPa load
held for 15 minutes by IEC 60811-2-1.
As shown by the hot creep test results in Table 1, the addition of
PDMS to either the base resin (sample A, a control) or a silane
grafted resin (sample B) does not produce the desired
cross-linking. Further comparative example (sample F), which
represent conventional moisture cure, either failed the hot creep
test after overnight storage with no external moisture exposure
(except what may have been trapped during compounding or in the
storage bag). Inventive samples D and E) in which OH-terminated
PDMS is added to a grafted resin and further reacted with a
catalyst produce effective crosslinking, either immediately during
the compounding step in the mixer (sample D) or produced a
thermoplastic compound, that could be shaped into a formed article
(e.g. a plaque) and when stored overnight in sealed bag produced a
homogenous crosslinking as shown by sample E. This is the desired
result.
The data also shows that it is possible to design compositions that
can be homogenously mixed to produce a thermoplastic material that
exhibit excellent crosslinking without the need for external
moisture exposure which is desirable for thick articles such as
molded parts or medium voltage and high voltage cable coating.
As a further confirmation of crosslinking, the composition of
sample E is repeated in another experiment, the sample made is
subjected to a DMA analysis, with a temperature sweep from
-150.degree. C. to 200.degree. C. As the data in the Figure shows,
compared to the ENGAGE 8200 base resin (melting point
.about.70.degree. C.), the modulus of the reactively-modified
PDMS-ENGAGE blend exhibits a plateau past the melting point,
indicating a good temperature resistance compared to the base
resin.
Electron microscopy shows drastically improved phase compatibility.
For example, sample E shows a predominantly single homogeneous
phase with some finely dispersed silicone domains. In contrast,
other compositions tested (samples A and C) show morphologies
typical of highly immiscible systems containing distinct, large
domains of silicone visible as droplets within the polyolefin
matrix.
Example 2
The data reported in Table 2 compares an LLDPE resin (0.7 MI, 0.920
g/cm.sup.3 density) grafted with 2% VTMS in the presence of 3%
silanol-terminated polydimethylsiloxane (OH-PDMS) versus a control
sample grafted under the same conditions without the OH-PDMS. Both
materials are first dried and then extruded on a wire (124 mil wire
O.D., 30 mil wall thickness) in the presence of a tin catalyst. The
insulation is removed, cured for 16 hours under ambient conditions
(23 C and 70% relative humidity), and then subjected to a hot creep
test at 200.degree. C., 15 min, 15 N/m.sup.2). The results show
that the comparative composition does not achieve 100% hot creep
elongation and 10% hot set targets. In contrast, the inventive
composition does pass the hot creep and hot set tests. The data
demonstrate the rapid cure rate at ambient conditions achieved with
the invention.
TABLE-US-00002 TABLE 2 Hot Creep and Hot Set Test Results of Test
Compositions Inventive Comparative Composition Composition Hot
Creep (% elongation) Pass Fail Hot Set (% elongation) Pass Fail
Example 3
The data set for this example is obtained on a sample taken from a
molded part. Molded part 10 (FIG. 2) comprises insulation layer 11
made out of an elastomer resin system which is grafted with
vinyltrimethoxysilane in the presence of OH-PDMS. Molded part 10 is
a 35 KV prototype connector comprising outer (12) and an inner (13)
semicon layers sandwiching insulation layer 11. Insulation layer 11
comprises a composition of this invention. The semicon layers are
first molded separately and peroxide-cured in a first molding step,
then mounted together in a second mold where the insulation layer
is injected between them. The insulation compound is premixed with
a tin catalyst masterbatch, injection is conducted in a fully
thermoplastic fashion, and the part is de-molded upon cooling (1-5
minutes molding time depending on the test run). Inner semicon
layer 13 is about 4 mm thick and covers most of the insulation,
except towards the ends. Outer semicon layer 12 is about 3.5 mm
thick and covers all the insulation layer, i.e. no external
exposure, and insulation layer 11 itself is about 11.6 mm thick.
Once received from the molding shop, the part is cut and three
samples are taken from the middle section of the insulation layer
for DMA testing. All samples are 1.9 mm thick. Starting from the
outside edge of the insulation layer, Sample 1 is about 3 mm inside
the layer, Sample 2 is about 5 mm inside the layer, and Sample 3 is
about 7 mm inside the layer. The part is handled under normal
shipping and lab storage conditions prior to testing, i.e. no
special heat or moisture exposure. The DMA data in FIG. 3 shows a
plateau modulus at a temperature above the melting point for each
of the samples or in other words, complete cure of the
material.
Although the invention has been described with certain detail
through the preceding specific embodiments, this detail is for the
primary purpose of illustration. Many variations and modifications
can be made by one skilled in the art without departing from the
spirit and scope of the invention as described in the following
claims.
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